P1.09-28 A Significant Discordance Between PANAMutyper™ and Targeted Deep Sequencing for Detecting EGFR Mutation in NSCLC

Abstract

Activating mutations in the tyrosine kinase domain of EGFR are predictive biomarkers for response to EGFR-tyrosine kinase inhibitor (TKI) therapy in non-small cell lung cancer (NSCLC). This study aimed to screen EGFR mutations by PNA clamping-assisted fluorescence melting curve analysis (PANAMutyper™) and targeted deep sequencing, and to evaluate the feasibility of targeted deep sequencing for detection of the mutations. We examined EGFR mutations in exons 18, 19, 20, and 21 using PANAmutyper™ for consecutive 2170 NSCLC tissues from November 2016 to March 2019. Of these, targeted deep sequencing was performed in 74 patients. EGFR mutations were identified in 46.4% (1007/2170); 479 (47.6%) had mutations at exon 19, 442(43.9%) at exon 21, 156(15.5%) at exon 20 (including 97 cases with T790M), and 46(4.6%) at exon 18. EGFR mutations were significantly more common in women (63.9%) than men (31.4%) (p <0.001), in adenocarcinoma (54.7%) compared to non-adenocarcinoma (15.3%) (p <0.001). 11.3% (11/97) of T790M mutations was identified in TKI-naïve patients. Interestingly, 27.3% (3/11) of the primary T790M existed alone without L858R or exon 19 deletions. We observed a significant discordance (24.3%: 18/74) of the EGFR mutation between PANAMutyper™ and targeted deep sequencing. Moreover, targeted deep sequencing revealed eight nonsynonymous single-nucleotide variations, ten insertion-deletion variations and one amplification in EGFR, which were not detectable by the PANAMutyper™. In 2 out of 18 discordant cases, EGFR mutations were detected only in PANAMutyper™. EGFR mutations were found frequently in non-adenocarcinomatous NSCLCs, emphasizing that testing for EGFR mutations is essential for all NSCLC patients. As T790M was found in TKI-naive patients, we cannot exclude the possibility of this mutation being a rare mutation existing from the beginning. Taken together, our study demonstrates that primary T790M alone exists and there is a significant discordance between PANAMutyper™ and targeted deep sequencing. The significance of these discrepancies should be carefully interpreted for the patient's treatment and clinical outcome.